Funds are requested to support an international workshop to determine the status of genetic and physical maps of human chromosome 21. The workshop, entitled, "Mapping Chromosome 21: Present Status and Future Strategies" will be held in Bethesda, Maryland on April 2-3, 1990 and will include twenty scientists from the USA as well as ten scientists from outside the USA. The primary focus of the meeting will be an analysis of data relating to the chromosome 21 map. The overall objective of the meeting is to highlight inconsistencies in the data, and to discuss strategies to expedite completion of the physical map of chromosome 21. Specific aims of the meeting will be to generate composite genetic and physical maps of chromosome 21 based on both published and unpublished data, and to define chromosome 21 specific "anchor loci." The meeting is intended to broaden collaborative efforts and foster more extensive interactions among the participants.